Suspending agent for the suspension polymerization of water-soluble monomers

ABSTRACT

A suspending agent useful in a water-in-oil suspension polymerization process comprises a fumed silica particulate having a hydrophobic character and a hydrophobic polymer. The suspending agent is useful in providing uniformly sized aqueous fluid absorbent polymer beads.

BACKGROUND OF THE INVENTION

This invention relates to suspension polymerization processes and inparticular to the suspending agents employed in said processes.

Various water-soluble polymers such as polyacrylamide and copolymers ofacrylamide with other anionic, cationic or nonionic monomers arewell-known to be precipitants or flocculants for many substratesincluding sewage, cellulosic fibers and fines for retention andfreeness, effluent waste for metal production, coal tailings and thelike. Such polymers are also known to exhibit superior thickeningproperties when said polymers are dissolved in aqueous media.Particularly well known for this purpose are the anionic polyacrylamidessuch as acrylamide/acrylic acid copolymers, including those prepared byhydrolysis of polyacrylamide. Such polymers are also very useful asfluid mobility control agents in enhanced oil recovery processes.

In the past, such polymers have been made available commercially aspowders or finely divided solids which must be subsequently dissolved inan aqueous medium in order to be used. Because such dissolution stepsare sometimes time consuming and often require rather expensive mixingequipment, it has become a common practice to formulate thewater-soluble polymers in water-in-oil emulsions wherein the polymer isdissolved in the dispersed aqueous phase. Such emulsions, as well asmethods for preparing them, are described in U.S. Pat. Nos. 3,284,393;3,826,771 and 4,052,353.

More recently, it has become desirable to provide aqueous fluidabsorbents by polymerizing water-soluble monomers such as acrylic acidin the presence of a crosslinking agent in order to provide highlyswellable polymeric materials. Such types of aqueous fluid absorbentsand materials provided therefrom are disclosed in U.S. Pat. Nos.4,511,477; 4,500,670; 4,424,247; and 4,293,609. Due to the nature of thecrosslinking agents employed in the preparation of such aqueous fluidabsorbents, the use of water-in-oil emulsion polymerization technologyin providing such types of polymeric materials has not been successfullyemployed to any great extent.

Suspension polymerization processes provide several advantages in thepreparation of water-soluble polymers and water-swellable polymers. Thereaction temperature and rate of reaction can be controlled due to theheat transfer properties attendant in such types of polymerizationprocesses. For example, the reaction temperature can be controlled bymeans of ebullient cooling. In addition, the polymer product so providedin water-in-oil suspension polymerization processes can be separatedfrom the oil phase using relatively efficient techniques such asfiltration or centrifugation. However, improvements in the preparationof water-soluble polymers and water-swellable polymers is clearlydesirable.

In view of the deficiencies of the prior art. it would be highlydesirable to provide a process for polymerizing water-soluble monomersusing water-in-oil suspension polymerization techniques; which processis capable of employing high quantities of monomer in the aqueous phasewithout substantial agglomeration of polymer, and which process can beemployed in providing crosslinked water-swellable polymers of acontrolled particle size.

SUMMARY OF THE INVENTION

The present invention is a suspending agent useful in suspensionpolymerization processes, said suspending agent comprising (1) aparticulate material comprising a hydrophobic character, and (2) apolymer having a substantially hydrophobic character said polymer havinghydrophobic moieties pendant from the backbone thereof.

The aforementioned suspending agent is particularly useful inwater-in-oil suspension polymerization processes.

In another aspect, the present invention is the oil phase useful inwater-in-oil suspension polymerization processes, said oil phasecomprising the aforementioned suspending agent.

In yet another aspect, the present invention is a water-in-oilsuspension polymerization process wherein water-soluble monomers arepolymerized, said process comprising

(1) providing an aqueous phase comprising water and at least onewater-soluble monomer, and

(2) providing an oil phase comprising an inert hydrophobic liquid andthe aforementioned suspending agent, and

(3) contacting the aqueous phase and the oil phase under conditions suchthat a water-in-oil suspension of polymer comprising polymerizedwater-soluble monomer is provided.

In addition to their utility as additives in drilling muds, fracturingfluids and fluid mobility control agents in enhanced oil recoverymethods, the water-soluble polymers prepared in accordance with thepractice of the present invention are also useful as flocculating agentsfor sewages, industrial wastes, mining streams such as coal slurries andmining effluents, as thickeners for coating formulations, as additivesfor the manufacture of paper, and in a variety of other uses common forsuch polymers prepared by other conventional polymerization methods.

Polymers comprising a crosslinked character, which crosslinked characterprovides a swellable character to the polymer, are useful as aqueousfluid absorbent compositions. For example, such aqueous fluid absorbentpolymer compositions can absorb several times their weight of an aqueousliquid, preferably more than about 15 times their weight in water. Suchcompositions can be employed in a wide variety of applications as aredisclosed in U.S. Pat. Nos. 4,424,247; 4,511,477; 4,293,609 and4,486,374.

Surprisingly, the use of the aforementioned suspending agent, whenemployed in suspension polymerization processes, can provide apolymerization product which exhibits a controlled particle sizedistribution. In addition, the polymerization products can beeffectively dried using relatively energy efficient techniques such assteam distillation or azeotropic distillation. Of particular interest isthe use of the suspending agent of this invention in providingwater-swellable polymer products of controlled particle size.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The present invention is practiced in the preparation of water-in-oilsuspensions containing any polymer provided from water-soluble monomers.Such suspensions are those wherein the dispersed phase is an aqueousphase having contained therein said polymer, and the continuous oilphase is a water-immiscible inert organic liquid. In suspensions of thisinvention, the percent of the aqueous phase to the oil phase is suchthat the suspensions contain from about 10 to about 70, preferably fromabout 40 to about 60, weight percent of aqueous phase. Advantageously,the suspension comprises preferably from about 90 to about 30, mostpreferably from about 60 to about 40, weight percent dispersed (i.e.,aqueous) phase based on the total weight of the suspension. The amountof polymer contained in the suspension can vary providing that theresulting suspension is stable, and is advantageously from about 10 toabout 50, more preferably from about 20 to about 40, weight percentpolymer based on the total weight of the suspension. In the suspensions,the weight ratio of water to polymer in the aqueous phase can vary andis desirably from about 0:100 to about 9:1, more preferably from about4:1 to about 1.5:1, and most preferably from about 2.33:1 to about0.67:1.

For the purposes of this invention, the water-soluble polymer containedin the aqueous phase of the suspension is one that forms athermodynamically stable mixture when combined with water. Thesemixtures form spontaneously and include true solutions in which theindividual polymer molecules are dispersed as well as micellar orcolloidal solutions wherein the polymer molecules are aggregated to someextent, but wherein such aggregates are no larger than colloidal size.Accordingly, such water-soluble polymers are generally homopolymers andcopolymers of water-soluble ethylenically unsaturated monomers.

Suitable water-soluble monomers include those that are at leastwater-miscible and that are preferably sufficiently water-soluble toform at least a 5 weight percent solution when dissolved in water andreadily undergo addition polymerization to form polymers that arewater-soluble. Exemplary water-soluble monomers include ethylenicallyunsaturated amides such as acrylamide, methacrylamide and fumaramide;their N-substituted derivatives such as 2-acrylamide-2-methylpropanesulfonic acid (AMPS® a registered trademark of The LubrizolCorporation), N-(dimethylaminomethyl)acrylamide as well asN-(trimethylammoniummethyl)acrylamide chloride andN-(trimethylammoniumpropyl)methacrylamide chloride; ethylenicallyunsaturated carboxylic acids such as acrylic acid, methacrylic acid,itaconic acid and fumaric acid; ethylenically unsaturated quaternaryammonium compounds such as vinylbenzyl trimethyl ammonium chloride,sulfoalkyl esters of unsaturated carboxylic acids such as 2-sulfoethylmethacrylate; aminoalkyl esters of unsaturated carboxylic acids such as2-aminoethyl methacrylate and 2-(N,N-dimethylamino)-ethyl methacrylateas well as the quaternized derivatives thereof such as acryloylethyltrimethyl ammonium chloride; vinyl amines such as vinyl pyridine andvinyl morpholine, diallyl amines and diallyl ammonium compounds such asdiallyl dimethyl ammonium chloride; vinyl heterocyclic amides such asvinyl pyrrolidone; vinylaryl sulfonates such as vinylbenzyl sulfonate aswell as the salts of the foregoing monomers. Of the foregoingwater-soluble monomers, acrylamide and combinations of acrylamide andacrylic acid are preferred. Homopolymers of acrylic acid can also beprepared. Homopolymers prepared from acrylamide and copolymers preparedfrom combinations thereof with other water-soluble monomers are morepreferred. Also preferred are polymers wherein the water-solublemonomers range from about 5 to about 99 mole percent of acrylamideand/or partially hydrolyzed acrylamide from about 1 to about 5 molepercent of other water-soluble monomers. Of particular interest arelightly crosslinked polymers such as polyacrylic acid polymers, sodiumpolyacrylate polymers, and copolymers of polymerized acrylic acid andsodium acrylate; which polymers are copolymerized with polyvinylmonomers such as trimethylolpropane triacrylate.

The water-immiscible oil phase of the suspension generally comprises atleast one inert hydrophobic liquid. Usually such liquid is an organicliquid such as a liquid hydrocarbon or substituted hydrocarbon.Preferred organic liquids are the halogenated hydrocarbons such asperchloroethylene, methylene chloride and the like as well as liquidhydrocarbon having from 4 to 15 carbons per molecule including aromaticand aliphatic hydrocarbons and mixtures thereof, e.g., benzene, xylene,toluene, mineral oils, liquid paraffins such as kerosene, naphtha andthe like. Of the foregoing organic liquids, the hydrocarbons are themore preferred, with aliphatic hydrocarbons being most preferred.

The suspension polymerization processes are performed by following thegeneral procedures described in the art as exemplified in U.S. Pat. Nos.4,340,706; 4,367,323 and 4,446,261, which are hereby incorporated byreference. In the process of this invention, an aqueous phase containingwater-soluble monomer(s) typically is dispersed in the inert hydrophobicliquid which contains the suspending agent of this invention. Typically,it is desirable to agitate the resulting composition. Factors such asthe rate of agitation of the composition control properties such as thedroplet or particle size of the suspended aqueous phase.

The suspending agent of this invention comprises two necessarycomponents; the particulate material having a hydrophobic character andthe polymer having a substantially hydrophobic character.

The particulate material comprising a hydrophobic character can bedescribed as an amorphous, highly oil dispersable, approximately micronsize, substantially water-insoluble particulate material. Typically, thesize of the particulate material ranges from less than 1 micron toseveral microns in diameter. The particulate material is most preferablyhydrophobic silicon dioxide such as that particulate material providedby the reaction of silica with polydimethyldichlorosilane. Other usefulparticulate materials include hydrophobic clays such as the cationicsurfactant treated bentonite clays. An example of a hydrophobic clay issold commercially as Bentone® 34 by N. L. Industries.

The polymer having a substantially hydrophobic character has hydrophobicmoieties pendant from the backbone thereof. The hydrophobic groups ofthe polymer having a substantially hydrophobic character are preferablypendant organic groups having hydrophobicities comparable to one of thefollowing: aliphatic hydrocarbon groups having at least about fourcarbons such as C₄ to C₂₀ alkyls and cycloalkyls; aromatic hydrocarbongroups such as alkylaryls wherein alkyl has one or more carbons,preferably 4 to 8 carbons; haloalkyls of 4 or more carbons, preferablyperfluoroalkyls; polyalkyleneoxy groups wherein alkylene is propylene orhigher alkylene and there is at least 1 alkyleneoxy unit per hydrophobicmoiety.

Suitable hydrophobic monomers include those which are (1)water-insoluble, i.e., less than about 0.4, preferably about 0.2, weightpart of the hydrophobic monomer will dissolve in 100 weight parts waterand (2) ethylenically unsaturated compounds having hydrophobic groups asdefined hereinbefore. Exemplary hydrophobic monomers include the higheralkyl esters of α,β-ethylenically unsaturated carboxylic acids such asdodecyl acrylate, dodecyl methacrylate, tridecyl acrylate, tridecylmethacrylate, tetradecyl acrylate, tetradecyl methacrylate, octadecylacrylate, octadecyl methacrylate, ethyl half ester of maleic anhydride,diethyl maleate, and other alkyl esters derived from the reactions ofalkanols having from 4 to about 20, preferably from 8 to about 20,carbon atoms with ethylenically unsaturated carboxylic acids such asacrylic acid, methacrylic acid, fumaric acid, itaconic acid and aconiticacid, and maleic anhydride; alkylaryl esters of ethylenicallyunsaturated carboxylic acids such as nonyl-α-phenyl acrylate,nonyl-α-phenyl methacrylate, dodecyl-α-phenyl acrylate anddodecyl-α-phenyl methacrylate; N-alkyl, ethylenically unsaturated amidessuch as N-octadecyl acrylamide, N-octadecyl methacrylamide, N,N-dioctylacrylamide and similar derivatives thereof; α-olefins such as octene-1,decene-1, dodecene-1 and hexadecene-1; vinyl alkylates wherein alkyl hasat least 8 carbons such as vinyl laurate and vinyl stearate; vinyl alkylethers such as dodecyl vinyl ether and hexadecyl vinyl ether; N-vinylamides such as N-vinyl lauramide and N-vinyl stearamide; andarylalkylstyrenes such as t-butyl styrene. Of the foregoing hydrophobicmonomers, the alkyl esters of acrylic acid, methacrylic acid, N-alkylacrylamides and N-alkyl methacrylamides wherein alkyl has from 8 to 20carbon atoms, the alkyl styrenes wherein alkyl has from 4 to 8 carbonssuch as t-butyl, are preferred. The alkylmethacrylates andalkylacrylates wherein alkyl has from 10 to 20 carbon atoms are morepreferred. Dodecyl methacrylate and N-dodecyl methacrylamide are themost preferred where hydrolysis is not a problem.

The polymer having a substantially hydrophobic character isadvantageously prepared by polymerizing the aforementioned hydrophobicmonomers and optionally other monomers such as hydrophilic monomers inan oil phase using conventional initiators or catalysts. The polymerstypically have molecular weights of about 1,000 to about 100,000. Theamount of hydrophilic monomer polymerized with the hydrophobic monomersdepends upon factors such as the types of water-soluble polymers whichare provided and typically ranges from greater than 0 to about 15percent. For example, the amount of hydrophilic monomer which ispolymerized in the polymer having the substantially hydrophobiccharacter can vary depending upon factors such as those attendant whenwater-soluble copolymers are prepared from two or more varying monomers.

The amount of components comprising the suspending agent can vary. Theamount of each component depends upon factors such as the desiredparticle size distribution of the polymer product. The amount of eachranges from about 5 to about 95 weight percent, relative to one another.

The amount of suspending agent employed depends upon factors such asthat amount necessary to provide a suspended aqueous phase in the oilphase while employing an amount which is economically low. The amounttypically ranges from about 0.05 to about 10 weight percent relative tothe amount of water-soluble monomer which is being polymerized.

The suspending agent is incorporated into the oil phase using a varietyof techniques. For example, it is desirable to contact the oil phasewith the suspending agent under conditions such as agitation.

Polymerization of the water-in-oil suspension of the water-solublemonomer(s) is advantageously effected under conventional conditions suchas described in U.S. Pat. Nos. 4,340,706; 4,367,323 and 4,446,261.Normally, such polymerization is practiced in the presence of apolymerization initiator capable of generating free-radicals.Preferably, this free-radical initiator is employed in amounts fromabout 0.01 to about 0.1 weight percent of initiator based on themonomers. Exemplary polymerization initiators include the inorganicpersulfates such as potassium persulfate, ammonium persulfate and sodiumpersulfate; azo catalysts such as azobisisobutyronitrile anddimethylazoisobutyrate; organic peroxygen compounds such as benzylperoxide, t-butylperoxide, diisopropylbenzene hydroperoxide, t-butylhydroperoxide; and compounds such as sodium borohydride. Of theseinitiators, the organic types such as t-butyl hydroperoxide arepreferred. In addition to the aforementioned ingredients, the suspensionpolymerization recipe optionally includes chain transfer agents,chelating agents, buffers, salts, and the like.

If desired, a crosslinking agent can be incorporated into thepolymerization process. The crosslinking agent can be incorporated intothe aqueous phase, the oil phase, or in the presence of both the aqueousphase and the oil phase. The crosslinking agent can be employed in anamount sufficient to provide to the polymerization product an effectiveincrease in molecular weight, or to provide to the polymerizationproduct a water-swellable character as is desirable in aqueous fluidabsorbent compositions, or to provide a hydrogel product. For example,oil-soluble polyvinyl crosslinking monomers can be incorporated into theoil phase. Examples of polyvinyl crosslinking monomers includeN,N'-methylene-bisacrylamide, divinylbenzene, diethylene glycoldiacrylate, propylene glycol dimethacrylate, allyl acrylate, diallylfumarate, trimethyloylpropanetriacrylate, and the like. Examples ofother crosslinking monomers include polyhaloalkanols; sulfoniumzwitterions; haloepoxyalkanes; polyglycidyl ethers; aminoepihalohydrinadducts; multivalent metal ions such as aluminum or calcium; glycidylacrylates; and the like. The amount of crosslinking agent depends upon avariety of factors, but typically ranges from about 0.01 to about 1percent based on the weight of the polymer.

After the polymerization reaction is complete, the suspension can beemployed in a variety of ways. For example, the suspension can be (a)employed as is, (b) treated using centrifugal techniques in order toseparate the polymer from the oil, (c) precipitated using agents such asmethanol or acetone, (d) filtered, or (e) spray dried.

The molecular weight of the water-soluble polymer or water-swellablepolymer is not particularly critical and may vary over a wide range.Typically, molecular weights range from about 100,000 to about 50million depending on the desired use of the polymer. Preferred polymershave weight average molecular weight in the range from about 2 to about25 million. It is understood that the molecular weights of thecrosslinked polymers can be essentially infinite.

The following examples are given to further illustrate the invention butnot to limit its scope. All parts and percentages are given by weightunless otherwise indicated.

EXAMPLE 1 A. Preparation of Laurylmethacrylate/Acrylic Acid Copolymer

To 795.4 g of laurylmethacrylate is added 4.64 g of glacial acrylic acidand 800 g of liquid hydrocarbon sold commercially as Isopar® M by Exxon.Then 0.8 g of 2,2'-azobis(2,4-dimethylvaleronitrile) which is soldcommercially as Vazo® 52 by E. I. duPont de Nemours Corporation isadded. The solution is agitated, purged with nitrogen for 1 hour andthen heated to 50° C. After 12 hours of heating, the temperature of thethickened solution is increased to 60° C. and held there for 2 hours. Itis then cooled and mixed with another 800 g of the aforementioned liquidhydrocarbon to give a 33 percent polymer solution.

B. Suspension Polymerization of Crosslinked Sodium Polyacrylate

131 g of glacial acrylic acid is mixed with 167 g of water. Then a 50percent aqueous solution of sodium hydroxide is added dropwise, whilekeeping the temperature less than 50° C. Addition is continued until thepH of the solution is 6.0. To this mixture is added 0.6 g of pentasodiumsalt or diethylenetriamine pentaacetic acid sold commercially asVersenex® 80 by The Dow Chemical Company, and the total weight of theaqueous phase is adjusted to 490 g with additional water.

The oil phase is prepared by adding 4.28 g of hydrophobic fumed silicasold as Aerosil® R-972 by Degussa and 12.82 g of 33.3 percent 99 molepercent laurylmethacrylate/1 mole percent acrylic acid copolymer in theliquid hydrocarbon to 432.9 g of the liquid hydrocarbon.

The aforementioned Aerosil® R-972 component is dispersed by mixing themixture with a Waring blender at medium agitation. The oil phase is thentransferred to a 1-liter reactor. The crosslinking agent, 0.4275 g oftrimethylolpropane triacrylate, is added to the oil phase. Then 0.0684 gof sodium persulfate and 0.0977 g of a 70 percent aqueous solution oft-butylhydroperoxide are added to the aqueous phase. The agitator on the1-liter reactor is set at 500 rpm and the aqueous phase is added quicklyto the oil phase. The reactor is purged with N₂ for 1 hour and initiatedby adding a nitrogen stream containing 1000 ppm SO₂ at a rate of 50cc/min through a dip tube. The reactor jacket is heated to 40° C. over a10-minute period. This controls the actual polymerization temperature toabout 50° C. After an hour, the jacket is heated to 60° C. andmaintained for an additional hour. The slurry is then cooled,centrifuged to remove excess liquid hydrocarbon and the product is airdried.

EXAMPLE 2

A water-soluble copolymer of acrylamide and acrylic acid is provided asfollows:

An aqueous phase is provided by mixing 241.8 g of aqueous acrylamidesolution (48 percent acrylamide) and 16.85 g of glacial acetic acid with69.8 g of water. To this mixture is added 0.28 g of the aforementionedVersenex 80 and enough of a 50 percent sodium hydroxide solution tobring the pH of the mixture to 6.5. Additional water is added to give atotal weight of the mixture of 350 g.

An oil phase is provided by adding 3.5 g of the aforementioned Aerosil®R-972 and 10.5 g of a 33 percent solution of a copolymer oflaurylmethacrylate and acrylic acid. The mole ratio oflaurylmethacrylate to acrylic acid is 95:5. The copolymer is blendedwith 336 g of the aforementioned Isopar M hydrocarbon.

To the aforementioned aqueous phase is added 0.7 g of isopropyl alcoholand 0.05 g of a 70 percent aqueous solution of t-butylhydroperoxide. Theoil phase is transfered to a 1-liter reactor and stirred at 300 rpm. Theaqueous phase is added to the oil phase and then the suspension ispurged for 1 hour with nitrogen. The polymerization is initiated byadding SO₂ at a flow rate of 0.05 cc/minutes. The reaction is held at50° C. for 1 hour and then heated to 60° C. for an additional hour.

The polymer is isolated by filtering off the hydrocarbon phase anddrying (i.e., the Isopar M) and drying the beads in a forced air dryerat 90° C. The product is a spherical free-flowing solid. The viscosityof 0.3 percent solution of the polymer in 3 percent sodium chloride at apH of 7 is 16 cps as determined using an Ostwald viscometer.

EXAMPLE 3

A copolymer comprised of 70 mole percent acrylamide and 30 mole percentacrylic acid is provided as follows:

An aqueous phase weighing 318 g is provided by mixing 165 g of a 49.4percent aqueous acrylamide solution with 35 g of glacial acrylic acidand 0.254 g of the aforementioned Versenex 80. To this solution is addedenough of a 50 percent sodium hydroxide solution to adjust the pH to6.5, 0.0727 g of tertiary butyl hydroperoxide and water to provide theaforementioned 318 g total weight.

An oil phase weighing 381.86 g is provided by mixing 3.18 g of theaforementioned Aerosil® R-972 composition with 318 g of apolylaurylmethacrylate polymer with 375.5 g of the Isopar M hydrocarbon.

The aqueous phase is added to the oil phase in a 1-liter reactor whileagitating at 450 rpm. The mixture is purged for 1 hour with nitrogen andinitiated by adding SO₂ at a flow rate of 0.05 cc/minute. Shortly afterinitiation the suspension fails, coalescing into large mass of polymer.

The aforementioned experiment is repeated, except that thepolylaurylmethacrylate polymer is replaced with 3.18 g of a copolymer of99 mole percent laurylmethacrylate and 1 mole percent acrylic acid. Thesuspension is agitated with SO₂ and heated to 50° C. for 1 hour. Thesuspension partially fails giving large chunks of agglomerated beads.

The above experiment is further repeated replacing the 1 mole percentacrylic acid/99 mole percent laurylmethacrylate copolymer, with 3.18 gof a 2.5 mole percent acrylic acid/97.5 mole percent laurylmethacrylatecopolymer. The polymerization proceeds smoothly. After polymerizing at50° C. for one hour, the product is isolated by filtering off thehydrocarbon (i.e., the Isopar M) and drying the beads. Microscopicexamination shows that the polymer consists of small agglomerates ofpolymer beads.

The above experiment is further repeated by replacing the 2.5 molepercent acrylic acid/97.5 mole percent laurylmethacrylate copolymer with3.18 g of a 5 mole percent acrylic acid/95 mole percentlaurylmethacrylate copolymer. The polymerization is run as describedhereinbefore. Microscopic examination shows that the product consists ofspherical polymer heads free from any signs of agglomeration.

EXAMPLE 4

A crosslinked polymer is provided as follows:

An aqueous phase is provided by mixing 116.4 g of glacial acrylic acid,0.53 g of the aforementioned Versenex 80, enough of a 50 percent aqueoussodium hydroxide solution to adjust the pH to 6 and enough water toprovide a 400 g total aqueous phase.

An oil phase weighing 400 g is provided by mixing 1.14 g of theaforementioned Aerosil® R-972, a copolymer of 99 mole percentlaurylmethacrylate and 1 mole percent acrylic acid, 0.456 g oftrimethylolpropanetriacrylate and 397.7 g of Isopar M hydrocarbon.

To the aqueous phase is added 0.0868 g of t-butyl hydroperoxide and0.0608 g of sodium persulfate to the aqueous phase which is in turnadded to a 1 liter reactor containing the oil phase. The agitator on thereactor is set at 450 rpm. The mixture is purged with nitrogen for 1hour and polymerization is then initiated at 25° C. by the addition ofSO₂ at the rate of 0.0833 cc/minute. The reaction is heated to 50° C.and is held at this temperature for 1 hour. The temperature is thenincreased to 60° C. and held there for an additional hour.

The reaction mixture is cooled to room temperature and the Isopar Mhydrocarbon is removed by filtration. The polymer beads are dried in aforced-air dryer at 90° C.

The water-retention capacity of the polymer so provided is determined tobe 75 g of a 0.9 percent aqueous sodium chloride solution per gram ofpolymer. The amount of extractable polymer is 2.5 percent. Theextractable polymer is determined by contacting a polymer sample in a0.9 percent aqueous sodium chloride solution and shaking for 16 hours.

The extractable polymer test is rerun except that a mixture of 0.9percent aqueous sodium chloride and polymer beads are sheared for 10seconds in a Waring blender at high speed. The sample is filtered andtitrated as usual. The extractables of this sample increase to 5.6percent.

The aforementioned polymerization process is repeated except that theSO₂ flow rate initiation is increased to 0.108 cc/minute. The polymer isisolated as described hereinbefore. The resulting polymer exhibits ahigher capacity while maintaining low extractables as indicated by aretention capacity of the 0.9 percent aqueous sodium chloride solutionof 90 g per gram of polymer and the polymer extractables value of 5.36percent and a further extractable of a similarly shear product of 11.8percent.

The aforementioned experiments indicate that the polymerizationconditions can affect polymer water-retention capacity. For example,increasing the SO₂ flow rate increases the capacity of the polymer. Theabove experiment also indicates that due to the fact that a higherpercentage of polymer extractables are provided in the shear beadexamples that it is believed that the copolymer beads are more highlycrosslinked near the surface of the particles.

EXAMPLE 5

A crosslinked polymer is provided as follows:

An aqueous phase weighing 308 g is provided by mixing 87 g of glacialacrylic acid, 0.228 g of the aforementioned Versenex 80, enough of a 50percent sodium hydroxide solution to adjust the pH to 8 and water.

An oil phase is provided by mixing 4.27 g of Aerosil® R-972, 1.42 g of a99 mole percent laurylmethacrylate/1 mole percent acrylic acidcopolymer, 0.456 g of diethyleneglycoldiacrylate and 336.76 g of IsoparM hydrocarbon.

The aqueous phase is mixed with 0.0468 g of a 70 percent solution oft-butyl hydroperoxide and 0.0468 g of sodium persulfate with the aqueousphase. This aqueous phase is added to the oil phase in a 1-literreactor. Agitation during addition is 450 rpm. The reactor is purgedwith nitrogen for 1 hour and then the polymerization is started byadding SO₂ at the rate of 0.0833 cc/minute. The polymerization is heldat 50° C. for 1 hour and then the mixture is heated to 60° C. for anadditional hour. The beads are separated by filtering off the excessIsopar M and dried in a forced-air oven at 90° C. The water-retentioncapacity of the beads so provided is 59 g of the 0.9 percent sodiumchloride solution per gram of polymer.

What is claimed is:
 1. A suspending agent useful in suspensionpolymerization processes, said suspending agent comprising (1) fumedsilicon dioxide, and (2) a copolymer of acrylic acid and laurylmethacrylate.